Recovery of combustible gases from furnaces in general and more particularly from converters

ABSTRACT

The combustible gases issuing from the mouth of a furnace, and more particularly of an oxygen-type converter, are collected by an exhaust conduit having its inlet end above the said mouth, but at a distance therefrom, and they are led into a combustion chamber where they are mixed with air withdrawn from the perimeter of the mouth by an annular air duct disposed around the inlet of the exhaust conduit and connected with the combustion chamber by an auxiliary air conduit provided with an air blower. The burnt gases from the combustion chamber are cooled, filtered and discharged outwardly by a gas blower which thus ensures the gas flow through the exhaust conduit. A portion of the cooled gases forced by the gas blower is derived into an annular gas duct disposed between the inlet end of the exhaust conduit and the annular air duct to form an inert gaseous screen which isolates the combustible gases from ambient air between the furnace mouth and the said inlet end.

United States Patent [191 Vicard Feb.4, 1975 RECOVERY OF COMBUSTIBLE GASES FROM FURNACES IN GENERAL AND MORE PARTICULARLY FROM CONVERTERS [75] Inventor: Pierre Georges Vicard, Lyon,

France [73] Assignee: S0cieteLab., Villeurbanne, France [22] Filed: Feb. 28, 1973 21 Appl. No.: 336,815

[30] Foreign Application Priority Data 1,284,435 12/1968 Germany ..266/l5 Primary Examiner-Gerald A. Dost Attorney, Agent, or FirmDowell & Dowell [57] ABSTRACT Mar. 3, 1972 France 72.08901 perimeter of the mouth by an annular air duct disposed around the inlet of the exhaust conduit and con- [52] US Cl 266/16, 423/210, 266/35 nected with the combustion chamber by an auxiliary [51] Int. Cl. C2lc 5/40 air conduit provided with an air blower. The burnt [58] Field of Search 266/15, 16, 35, 36 P; gases from the combustion chamber are cooled, fil- 122/7 A, 7 B; 423/210 tered and discharged outwardly by a gas blower which thus ensures the gas flow through the exhaust conduit. [56] References Cited A portion of the cooled gases forced by the gas blower UNITED STATES PATENTS is derived into an annular gas duct disposed between 3 154 406 10/1964 Allard 266,16 x the inlet end of the exhaust conduit and the annular 3357820 12/1967 266,35 X air duct to form an inert gaseous screen which isolates 313721917 3/1968 Richardson 266/15 the Combustible gases from ambient air between the 3,727,587 4/1973 Nebgen 122/7 A furnace mou h and the said inlet end.

FOREIGN PATENTS OR APPLICATIONS 5 Claims, 5 Drawing Figures 4641407 5/l967 Japan 266/16 RECOVERY OF COMBUSTIBLE GASES FROM FURNACES IN GENERAL AND MORE- PARTICULARLY FROM CONVERTERS The present invention relates to the recovery of combustible gases from furnaces in general and more particularly from converters such as those used in the steel industry and in which the metal in treated by air or preferably by substantially pure oxygen.

It is known that such furnaces emit large quantities of dust-laden carbon monoxide which is generally removed by means of a hood disposed above the furnace mouth. But ambient air is also induced into the hood through the space which must be left between the latter and the furnace mouth, and therefore carbon monoxide burns within the hood and in the exhaust conduit associated therewith. Owing to the elevated initial temperature of the gases issuing from the furnace, more particularly with converters of the oxygen type, this combustion generates extremely high temperatures which rapidly damage the mouth of the furnace, the hood and the exhaust conduit in spite of the water cooling systems with which they may be provided.

It has been proposed to avoid these drawbacks by providing around the inlet of the hood one or more ducts, and preferably a single annular duct, which withdraw air from the perimeter of the furnace mouth, this duct or these ducts being connected with the hood at a point thereof spaced from the said inlet. The combustion of carbon monoxide then only takes place in the portion of the hood remote from the furnace mouth, which avoids excessive temperatures in the vicinity of the latter, but these temperatures then occur in the hood and in the exhaust conduit which are therefore frequently to be repaired.

In accordance with the present invention the air induced into the auxiliary duct or ducts is only mixed with the combustible gases within a combustion chamber located at the end of the exhaust conduit remote from the furnace mouth.

In the accompanying drawings:

FIG. 1 is a diagrammatical view with parts in section, illustrating a plant according to the invention.

FIG. 2 is a fragmental longitudinal section of the exhaust conduit in the plant of FIG. 1.

FIG. 3 is an enlarged cross-section taken along line Ill-Ill of FIG. 2.

FIGS. 4 and 5 are fragmental views similar to FIG. 1, but illustrating modifications.

Referring to FIG. 1, reference numeral 1 designates a converter rockable about an axis in the conventional manner, between three different positions, namely a vertical operating position illustrated in full lines, a loading position la and a pouring position lb both indicated in dash lines. At the vertical position the upper mouth of the converter receives a lance 2 through which oxygen is injected into the molten metal. A considerable quantity of combustible dust-laden carbon monoxide then exhausts at a quite high temperature from the converter mouth and should be recovered.

For this purpose the conventional protective hood 3 provided above the converter mouth at the oxygen injecting position comprises the inlet end of an appropriately water-cooled exhaust conduit 4 the other end of which opens into a combustion chamber Slocated at a distance from the converter. This chamber is preferably formed of a gas furnace associated with a steam boiler of any description. The relatively cooled burnt gases from chamber 5 reach a dust collecting filter 6 and they are discharged outwardly through a chimney 7 by a blower 8.

The inlet end of exhaust conduit 4 is surrounded by an annular wall 9 which defines an annular duct I0 opening above the converter mouth. This duct is connected with the outlet of blower 8 by means of a conduit 11 provided with an appropriate valve device 12.

The annular wall 9 is in turn surrounded by another annular wall 13 which defines with wall 9 another annular duct 14 connected through valves such as 15 with an upper air collecting chamber 16. The latter is itself connected with the low pressure side of an air blower 18 the high pressure side of which is connected with the combustion chamber 5 by a conduit 19. It may be considered that duct 14, chamber 16, conduits l7 and 19 form an auxiliary air conduit through which ambient air may be forced into the combustion chamber for burning the combustible gases supplied by the exhaust conduit 4.

A first lateral auxiliary hood 20 is disposed above the loading position la of the converter mouth, this hood being connected with the air collecting chamber 16 through valves such as 21. Another auxiliary lateral hood 22 is disposed above the pouring position lb of the converter mouth and it is also connected with air chamber 16 through valves such as 23.

When the converter is at the vertical position of FIG. 1, oxygen being injected into the molten metal through lance 2, valves 21, 23 are closed and valves 15 are open. The dust-laden combustible gases are collected by exhaust conduit 4 and drawn into combustion chamber 5 under the action of blower 8, while ambient air is induced into the air duct 14 and forced into chamber 5 by blower 18. Of course blower 18 should supply the quantity of comburent air required for completaly burning the gases issuing from the converter and blower 8 should be so adjusted to collect all the gases generated by the converter. When this is obtained substantially no combustion takes place within ducts l0 and 4, and therefore hood 3 together with the exhaust conduit 4 are not submitted to the quite excessive temperature which would otherwise result from the combustion of the carbon monoxide generated by the converter, this combustion only taking place in the combustion chamber 5 which may comprise refractory walls conveniently lined with water tubes and which only receives gases which have been somewhat cooled by the water jacket of the exhaust conduit.

The burnt gases issuing from the combustion chamber 5 are preferably further cooled as for instance by water jets within the dust filter 6. A portion of the cooled and filtered gases is derived through conduit 11 and valve 12 and it is thus caused to flow through duct 10 at the outlet of which it forms around the mouth of the converter and the inlet end of exhaust conduit 4 an inert gaseous screen which prevents any ingress of comburent air into the exhaust conduit and any ingress of combustible gas into the auxiliary air duct. The gases which form this screen are collected in part by conduit 4, in part by duct 14.

When the oxygen injecting step is ended, the lance 2 is withdrawn and the converter is rocked to position lb (pouring step). Valves 15 are closed and valves 23 are open. The residual dust-laden gases issuing from the furnace mouth are then collected by the second auxiliary hood 22 together with ambient air and are forced into the combustion chamber which preferably comprises a pilot burner.

The converter is thereafter brought to the loading position la in order to receive a fresh load of molten metal. During this step valves 23 are closed and valves 21 are open, the gases and fumes from the converter being therefore recovered by the first lateral hood 20.

FIGS. 2 and 3 illustrate a particular arrangement of the exhaust conduit 4. The latter is cooled in the conventional manner by means of a water jacket in an intermediate annular space 25 defined by two spaced walls 4a and 4b, the cooling water being injected tangentially into this intermediate space, as for instance by a number of nozzles such as 24. Experience shows that the rotational movement of the water layer is of advantage for an efficient cooling but that in actual practice this movement disappears rapidly along the conduit. This is due to the fact that in the bends the velocity of the water mass is irregular, which generates whirls. This is avoided in FIGS. 2 and 3 by increasing the radial width of the annular space 25 in a manner more or less inversely proportional to the radius of curvature of the bend. The rotational velocity may thus be maintained substantially constant and therefore the rotating movement extends up to the combustion chamber along the whole length of the conduit.

FIG. 4 illustrates a modification wherein the cooled and filtered gases recycled through conduit 11 and duct are no more used for forming an inert screen, but are introduced into the inlet end of the exhaust conduit 4 through holes 10a in order to form a relatively cool protective layer against the wall of the latter, the lower end of duct 10 being closed.

FIG. 5 shows another modification wherein the recycled gases are introduced into the inlet air duct 14 through holes 10b, the lower end of duct 10 being here again closed. This admission of inert gases into the auxiliary air conduit and into the combustion chamber 5 permits of reducing the quantity of comburent air in the said chamber, when required, by merely acting on valve 12.

It is obvious that the arrangements of FIGS. 1, 4 and 5 could be combined, if desired.

1 claim: 3

l. A plant for the recovery of combustible gases issuing from the mouth of furnaces in general and more particularly of converters comprising:

- an exhaust conduit having an inlet end and an outlet end, with said inlet end being disposed above the furnace mouth to collect combustible gases issuing therefrom;

- a combustion chamber separate from said exhaust conduit with the outlet end of said exhaust conduit opening into said chamber;

- an auxiliary air conduit having an annular inlet located around the inlet of said exhaust conduit above the furnace mouth to withdraw ambient air from the perimeter of said mouth, and an outlet end opening into said combustion chamber to sup ply same with comburent air to cause combustion of said combustible gases within said combustion chamber, thus producing burnt gases therein;

- means to discharge outwardly said burnt gases from said combustion chamber;

- gas propelling means to cause said combustible gases to flow through said exhaust conduit into said combustion chamber and said burnt gases from same to said discharge means;

- air propelling means to cause air to flow through said auxiliary air conduit into said combustion chamber;

- said gas propelling means comprising a first blower having its low pressure side connected with said combustion chamber;

- and said air propelling means being formed of a second blower disposed in said auxiliary air conduit.

2. A plant for the recovery of combustible gases issuing from the mouth of furnaces in general and more 5 particularly of converters comprising:

an exhaust conduit having an inlet end and an outlet end, with said inlet end being disposed above the furnace mouth to collect combustible gases issuing therefrom;

- a combustion chamber separate from said exhaust conduit with the outlet end of said exhaust conduit opening into said chamber;

- an auxiliary air conduit having an annular inlet located around the inlet of said exhaust conduit above the furnace mouth to withdraw. ambient air from the perimeter of said mouth,- and an outlet end opening into said combustion chamber to supply same with comburent air to cause combustion of said combustible gases with said combustion chamber, thus producing burnt gases therein;

- means to discharge outwardly said burnt gases from said combustion chamber;

- gas propelling means to cause said combustible gases to flow through said exhaust conduit into said combustion chamber and said burnt gases from same to said discharge means;

- air propelling means to cause air to flow through said auxiliary air conduit into said combustion chamber; 7

- an annular gas recycling duct disposed between the inlet end of said exhaust conduit and the annular inlet of said auxiliary air conduit, said duct also opening above the furnace mouth;

- and means to introduce into said duct a portion of the burnt gases from said combustion chamber to form an inert annular gaseous screen between the combustible gases issuing from the furnace mouth and the ambient air withdrawn by the annular inlet of said auxiliary air conduit.

3. In a plant as claimed in claim 1 for a furnace tiltable between a loading position, a blowing position and a pouring position:

- a first auxiliary hood disposed above the mouth of the furnace when same is at its loading position;

- a second auxiliary hood disposed above the mouth of the furnace when same is at its pouring position;

- the inlet of said exhaust conduit being disposed above the mouth of the furnace when same is at its blowing position;

- and valve means to selectively connect said auxiliary air conduit respectively with the annular inlet of same, with said first auxiliary hood or with said second auxiliary hood.

4. A plant for the recovery of combustible gases issuing from the mouth of furnaces in general and more particularly of converters comprising:

an exhaust conduit having an inlet end and an outlet end, with said inlet end being disposed above the furnace mouth to collect combustible gases issuing therefrom;

a combustion chamber separate from said exhaust conduit with the outlet end of said exhaust conduit opening into said chamber;

an auxiliary air conduit having an annular inlet located around the inlet of said exhaust conduit above the furnace mouth to withdraw ambient air from the perimeter of said mouth, and an outlet end opening into said combustion chamber to supply same with comburent air to cause combustion of said combustible gases within said combustion chamber, thus producing burnt gases therein; means to discharge outwardly said burnt gases from said combustion chamber;

gas propelling means to cause said combustible gases to flow through said exhaust conduit into said combustion chamber and said burnt gases from same to said discharge means;

and air propelling means to cause air to flow through said auxiliary air conduit into said combustion chamber;

said exhaust conduit being formed with at least one bent portion having a radius of curvature and being double walled to define a cooling water jacket, with the width of said water jacket being substantially inversely proportional to the radius of curvature of said bent portion, and said plant further comprising means to inject water tangentially into said water jacket.

5. A plant for the recovery of combustible gases issuing from the mouth of furnaces in general and more particularly of converters, comprising:

- means to withdraw the combustible gases above the furnace mouth;

- means to withdraw ambient air from the perimeter ent air.

. UNITED STATES PATENT OFFICE I CERTIFICATE OF CORRECTION PATENT NO. 3, 863,906

DATED February 4, 1975 INVENTOR(S) 1 PIERRE GEORGES VICARD It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

The priority claimed is March 9, 1972,

not March 3 as printed on the patent.

Signed and Sealed this Twenty-seventh Day Of July 1976 [SEAL] Attest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer (mnmissinner oj'Parents and Trademarks UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3, 863,906

DATED February 4, 1975 INVENTOR(S) PIERRE GEORGES VICARD It is certified that error appears in the ab0ve-identified patent and that said Letters Patent are hereby corrected as shown below:

The priority claimed is March 9, 1972,

not March 3 as printed on the patent.

En'gncd and Sealed this Twentyseventh Day Of July 1976 [SEAL] A ttes t:

RUTH C. MASON C MARSHALL DANN Arresting Officer (mnmissiuner ofPatents and Trademurkx 

1. A plant for the recovery of combustible gases issuing from the mouth of furnaces in general and more particularly of converters comprising: - an exhaust conduit having an inlet end and an outlet end, with said inlet end being disposed above the furnace mouth to collect combustible gases issuing therefrom; - a combustion chamber separate from said exhaust conduit with the outlet end of said exhaust conduit opening into said chamber; - an auxiliary air conduit having an annular inlet located around the inlet of said exhaust conduit above the furnace mouth to withdraw ambient air from the perimeter of said mouth, and an outlet end opening into said combustion chamber to supply same with comburent air to cause combustion of said combustible gases within said combustion chamber, thus producing burnt gases therein; - means to discharge outwardly said burnt gases from said combustion chamber; - gas propelling means to cause said combustible gases to flow through said exhaust conduit into said combustion chamber and said burnt gases from same to said discharge means; - air propelling means to cause air to flow through said auxiliary air conduit into said combustion chamber; - said gas propelling means comprising a first blower having its low pressure side connected with said combustion chamber; - and said air propelling means being formed of a seCond blower disposed in said auxiliary air conduit.
 2. A plant for the recovery of combustible gases issuing from the mouth of furnaces in general and more particularly of converters comprising: - an exhaust conduit having an inlet end and an outlet end, with said inlet end being disposed above the furnace mouth to collect combustible gases issuing therefrom; - a combustion chamber separate from said exhaust conduit with the outlet end of said exhaust conduit opening into said chamber; - an auxiliary air conduit having an annular inlet located around the inlet of said exhaust conduit above the furnace mouth to withdraw ambient air from the perimeter of said mouth, and an outlet end opening into said combustion chamber to supply same with comburent air to cause combustion of said combustible gases with said combustion chamber, thus producing burnt gases therein; - means to discharge outwardly said burnt gases from said combustion chamber; - gas propelling means to cause said combustible gases to flow through said exhaust conduit into said combustion chamber and said burnt gases from same to said discharge means; - air propelling means to cause air to flow through said auxiliary air conduit into said combustion chamber; - an annular gas recycling duct disposed between the inlet end of said exhaust conduit and the annular inlet of said auxiliary air conduit, said duct also opening above the furnace mouth; - and means to introduce into said duct a portion of the burnt gases from said combustion chamber to form an inert annular gaseous screen between the combustible gases issuing from the furnace mouth and the ambient air withdrawn by the annular inlet of said auxiliary air conduit.
 3. In a plant as claimed in claim 1 for a furnace tiltable between a loading position, a blowing position and a pouring position: - a first auxiliary hood disposed above the mouth of the furnace when same is at its loading position; - a second auxiliary hood disposed above the mouth of the furnace when same is at its pouring position; - the inlet of said exhaust conduit being disposed above the mouth of the furnace when same is at its blowing position; - and valve means to selectively connect said auxiliary air conduit respectively with the annular inlet of same, with said first auxiliary hood or with said second auxiliary hood.
 4. A plant for the recovery of combustible gases issuing from the mouth of furnaces in general and more particularly of converters comprising: - an exhaust conduit having an inlet end and an outlet end, with said inlet end being disposed above the furnace mouth to collect combustible gases issuing therefrom; - a combustion chamber separate from said exhaust conduit with the outlet end of said exhaust conduit opening into said chamber; - an auxiliary air conduit having an annular inlet located around the inlet of said exhaust conduit above the furnace mouth to withdraw ambient air from the perimeter of said mouth, and an outlet end opening into said combustion chamber to supply same with comburent air to cause combustion of said combustible gases within said combustion chamber, thus producing burnt gases therein; - means to discharge outwardly said burnt gases from said combustion chamber; - gas propelling means to cause said combustible gases to flow through said exhaust conduit into said combustion chamber and said burnt gases from same to said discharge means; - and air propelling means to cause air to flow through said auxiliary air conduit into said combustion chamber; said exhaust conduit being formed with at least one bent portion having a radius of curvature and being double walled to define a cooling water jacket, with the width of said water jacket being substantially inversely proportional to the radius of curvature of said bent portion, and said plant further comprising means to inject water tangentially into said water jacket.
 5. A plant for the recovery of coMbustible gases issuing from the mouth of furnaces in general and more particularly of converters, comprising: - means to withdraw the combustible gases above the furnace mouth; - means to withdraw ambient air from the perimeter of the furnace mouth; - means to mix said gases and said air in a separate combustion chamber to cause combustion of said combustible gases within said combustion chamber, thus producing burnt gases; - means to discharge outwardly said burnt gases from said combustion chamber; and means to derive a portion of said burnt gases from said combustion chamber and to form with said derived burnt gases an inert gaseous screen around said combustible gases as same issue from said furnace to isolate said combustible gases from ambient air. 